Graphene-Based Standalone Solar Energy Converter for Water Desalination and Purification

Transcription

1 Supporting Information for Graphene-Based Standalone Solar Energy Converter for Water Desalination and Purification Yang Yang,, Ruiqi Zhao,, Tengfei Zhang,, Kai Zhao,, Peishuang Xiao,, Yanfeng Ma,, Pulickel M. Ajayan, Gaoquan Shi and Yongsheng Chen*,, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry, and The National Institute for Advanced Materials,Nankai University, Tianjin, , China. Department of Materials Science and Nano Engineering, Rice University, Houston, Texas 77005, United States. Department of Chemistry, Tsinghua University, Beijing , China This PDF file includes: Instrument and Measurement Conditions Supporting Discussion Supporting Figures and Tables Supporting Movie Captions References 1

2 Instrument and Measurement Conditions The O3 treatment was carried out using a UV ozone system (42a-220, Jelight Company, Inc., USA). The UV-Vis diffuse reflectance spectra (UV-Vis, DRS) were recorded by a Cary 5000 UV-visible-NIR spectrophotometer employing a lab-sphere diffuse reflectance accessory in the range of nm. Scanning electron microscopy (SEM) images were obtained on a FEI NanoSem 430 field emission scanning electron microscope using an accelerating voltage of 20 kv. The contact angles for water was measured using an instrument (G10, Krϋss Optronic GmbH, Germany and EARKZ-SPCA, HARKE Company, China). The contents of Na +, K +, Ca 2+ and Mg 2+ were measured by atomic emission spectrometry with inductively coupled plasma (ICP-AES) using IRIS Intrepid apparatus (ThermoFisher Corp.). Specific surface area of the material was measured by nitrogen adsorption/desorption at 77 K on a Micromeritics ASAP 2020 apparatus, using the Brunauer-Emmett-Teller (BET) method and the results show that the material has a BET surface area ~218 m 2 g -1. The microwave irradiation experiment was carried out on a microwave reactor (CEM, Discover SP, 2450 MHz). Supporting Discussion Thermal conductivity The 3DG thermal conductivity of W m -1 K -1 is measured in dry state. 1 And the thermal conductivity of this material in wet state is measured about 0.45 W m -1 K -1 with 2

3 an infrared (IR) microscope (Figure S18) following the literature published previously. 2 The thermal conductivity compared with other materials is list below (Table S3) showing that our material is comparable among the materials reported before. Specific rate calculation The specific rate (defined as specific rate = Water production rate weight of 3DG ) of the 3DG is compared with some reported state-of-the-art bulk systems (nanoparticle absorber, carbon black, and volumetric absorber) in literatures and is presented in Figure 1c. All the systems are non-vacuum and under 1 sun illumination. Reusability test Salt water: The test was carried out under 1 and 10 sun, respectively. And each cycle lasted for 2 hours. Under 10 sun, for each cycle, the 3DG sample was put on the surface of the salt water (Na + : mg L -1 ), and the 3DG was floating on the surface of the water. After illuminating for 2 hours, the water was evaporated and the sample shank with the salt crystal on its surface. After 20 cycles, the final Na + concentration is estimated up to mg L -1. The concentration of Na + was measured by atomic emission spectrometry with inductively coupled plasma (ICP-AES). And the sample after the 20 cycle was freeze-dried directly with the high concentration of the salt water. The structure of the 3DG after the 20 cycles was shown in Figure S5. 3

4 Sewage water: The test was carried out under 1 sun. And each cycle lasted for 2 hours. The concentration of the methyl orange is 1 g L -1. The result was shown in Figure S19. Microwave irradiation experiment The 3D graphene material (20 mg) was placed in the reactor with water in a microwave reactor (CEM Discover, 2450 MHz). After the irradiation of the microwave, the water was evaporated to the vapor, and the mass loss was recorded by the balance. Meanwhile, a controlled experiment using water without 3D graphene under the microwave irradiation was also carried out. Heat loss The heat loss by absorber consists of three losses: (1) radiation, (2) convection, and (3) conduction. The details of calculation are shown below. Radiation. It is assumed that the absorber has maximum emissivity of For radiation loss to an ambient temperature of about 20 C under 10 kw m -2, the radiation loss was calculated by the Stefan Boltzmann equation: E R = εaσ(t 4 T 4 ) (1), where ER denotes heat flux, ɛ is the emissivity, A is the surface area (1.77 cm 2 ), σ is the Stefan Boltzmann constant ( W m 2 K 4 ), T is thec of absorber (80 C), and T is the ambient temperature in our experiment (20 C). Therefore, based on Eq. 4

5 S1, we can calculate that the radiation heat loss of the device accounts for 4.4% of all irradiation energy. Convection. The convection loss was calculated by Newton s law of cooling Q = Ah(T T ) (2), where Q denotes the heat, h is the convection heat transfer coefficient, A is the surface area (1.77 cm 2 ). The convection heat transfer coefficient is about 5 W m 2 K 1. Therefore, based on Eq. S2, we can calculate that the convection heat loss of the device accounts for 2.9% of all irradiation energy. Conduction. The conduction loss was calculated based on Q = Cm T (3), where Q denotes the heat, C is the specific heat capacity of water (4.2 J g -1 C -1 ), m is the water weights (3 g), and ΔT (14 C) is the elevated water temperature within t seconds (3600 s). Therefore, based on Eq. S3, we can calculate that the conduction heat loss of the device accounts for 2.7% of all of the energy. Modelling Figure 3a shows the heat transfer processes involved in a floating solar steam generator, including radiative and convective heat loss to the ambient and conductive heat loss to the underlying water. The evaporation rate ṁ can be expressed as ṁh fg = Aαq solar εaσ(t 4 T 4 ) Ah(T T ) Aq water (4) 5

6 And the energy conversion efficiency (η) is defined as η = ṁh fg Aq solar (5) where ṁ is the water evaporation rate, hfg is the enthalpy change of liquid water to vapor, qsolar is the solar flux per area, and A is the total area of the receiver. So based on the Eq. S4 and S5, efficiency can be expressed as η = α εσ(t4 T 4 ) h(t T ) q water (6) q solar q solar q solar In order to simplify the discussion, a cubic is built as a building-block which is composed of single-layer graphene. The size of the building-block is a, the density of the bulk cross-linked 3DG is 1 mg cm -3 in the actual situation, the 2D mass density of graphene is mg cm -2. In a cubic of 1 cm 3, the total graphene mass can be simply estimated as: a 2 1 a 3 3 = 1 1 (7) a is 2.38 μm. From the transmittance of multi-layer graphene (by neglecting the interlayer interaction) in reference, 3 T = ( N) 2 (8) h = (N 1) 2.28 (9) Where T is transmittance of multi-layer graphene, N is number of graphene layers and h is the thickness of the 3DG. 6

7 The transmittance of the 3D Graphene can be expresses as: T = ( h )2 (10) The predicted transmittance of the different thicknesses of 3DG is validated with the experimental data. In the case of our materials under the 10 kw m -2, the reflection is ~3%, the ambient temperature is 20 ºC, and the final surface temperature is 80 ºC, ɛ is 0.97, σ is W m -2 K -4, h is 5 W m -2 K -1. In the cases of sample with different thicknesses, the underlying water has an increase of ~14 ºC, so the conductive heat loss is all 2.7% approximately η = 0.87 ( h )2 (11) The theoretical model produced good agreement with the experimental data from the water-harvesting experiment, as shown in Figure 3c. Application demo As shown in Figure S15, a practical device was setup to for the desalination and sewage treatment. The 3DG material and salt (waste) water were placed in the middle of the chamber. The salt water contains four ions mimicking the sea water for the desalination. The contents of Na +, K +, Ca 2+ and Mg 2+ were measured by atomic emission spectrometry with inductively coupled plasma (ICP-AES) using IRIS Intrepid apparatus (ThermoFisher Corp.) and the concentration is shown in Figure 4a. The concentration of the methylene orange and methylene blue is 1 g L -1 and 0.05 g L -1, respectively. To confirm that the excellent sewage treatment performance of the 3DG 7

8 benefits from solar-thermal conversion, not the absorption of the contaminant, a 12- hour continuous standing test of 3DG with sewage (methyl orange solution) was carried out showing that absorption is not the main factor (Figure S20). 8

9 Supporting Figures and Tables Figure S1 N2 adsorption/desorption analysis of our 3D Graphene with a BET surface area of 218 m 2 g -1. Figure S2 SEM image of the structure. Such structure benefits efficient light absorption through the multiscattering effect and the fluid flowing through the interconnected pores. Inset is the optical image of the 3DG material. 9

10 Figure S3 The experimental set-up. (a) The evaporation rate is measured by a high accuracy balance and then real-time communicated to a laptop computer for the evaluation of the evaporation rate and solar-thermal conversion efficiency. (b) and (c) are the vertical and side view of the test chamber, respectively. Figure S4 The water evaporation rate of 3D Graphene with different size under 1 sun irradiation. 10

11 Figure S5 Water evaporation rate with different humidity under 1 sun irradiation. Figure S6 The surface temperature of the water with 3DG under solar light irradiation (1 kw m - 2 ). 11

12 Figure S7 Water evaporation over time with different bulk water quantities under 10 kw m -2. Figure S8 The SEM images of 3DG after 20 cycles. The structure has barely changed in spite of the NaCl crystal on the surface. 12

13 Figure S9 The mass change of water under 8 kw m -2 over time. Figure S10 Photographs of the 3DG in the methylene blue solution. After remove the pressure, the sample can recover to its initial dimension. Scale bar, 2 cm. 13

14 Figure S11 Photographs of the 3DG in the air. After remove the pressure, the sample can recover to its initial dimension. Scale bar, 2 cm. Figure S12 (a) and (b) are the efficiency (left-hand side axis) and corresponding water evaporation rate (right-hand side axis) under different optical concentrations with the different wavelengths of the monochromatic light 450 nm and 532 nm, respectively. 14

15 Figure S13 Solar-thermal performance under microwave (2450 MHz) with different power densities of 20 W (a), 60 W (b) and 80 W (c), respectively. Figure S14 The experimental transmittance vs different thickness of the 3DG. The predicted transmittance profile is also included, showing good agreement. 15

16 Figure S15 The homemade device for the clean water generation. Figure S16 The scaled-up open device on the roof of a building. 16

17 Figure S17 The scaled-up covered device. Figure S18 The IR image of the 3D Graphene filled with water. The thermal conductivity of the reference material (glass, 4 mm) is 0.5 W m -1 K

18 Figure S19 The reusability of 3DG under 1 kw m -2 solar irradiation for 10 cycles with a methyl orange solution (1 g/l), mimicking the sewage water. Each cycle was tested for 2 hours. Figure S20 Optical images of the methyl orange solution with 3DG before and after 12-hour s standing without light illumination, mimicking the treatment of sewage water. 18

19 Supporting Tables Table S1. The solar-thermal performance and structure properties of materials under 1 kw m -2. Materials Evaporation rate (kg m -2 h -1 ) a) This represents the components of the material for solar-thermal conversion. b) The experiment is test in a NaCl solution (3.5 wt. %). c) The efficiency of this material is the external solar-heat conversion efficiency as 92.1%±3.2%, not shown here. η (%) Thermal insulator material Component a) 3DG Exfoliated graphite(dls) Carbon foam 2 VAGSM Glass fiber/ps foam 3 RGO/MCE Carbon-coated paper 6 3D-CG 7 Mixed cellulose esters EPS foam Cellulose (NFC) GO PS foam-cellulose 3 RGO-SA-CNT CNT-Silca Silica 2 PPy-coated SS stainless steel mesh 2 N-doped graphene Mxene-PVDF-PS PVDF-PS foam 3 HCuPO-PDMS b) Al NP/AAM AAM 2 Au/D-NPT Nanoporous alumina 2 rgo-mnps b) Ti2O c) Cellulose membrane 2 Au AAO

20 Table S2. The concentration (mg L -1 ) of ions of the mimic sea water before and after desalination obtained by atomic emission spectrometry with inductively coupled plasma (ICP-AES) analysis. Ion Before After Distilled water Na K Mg Ca Table S3.Thermal conductivity of materials in literatures and our work. Materials Dry state Wet state Insulator (W m -1 K -1 ) (W m -1 K -1 ) (W m -1 K -1 ) Ref 3DG / Our work 3D-CG / 7 DLS Exfoliated Graphite / Carbon Foam / 2 VAGSM / / 4 rgo/mce / / 5 GO 0.2 / / 8 RGO-SA-CNT 0.05 / / 9 N-doped Graphene 52±6 / / 12 Carbon-Coated Paper / / CNT-Silca / / Ti2O3 / / Note, the materials are abbreviated following the previous literatures. Supporting Movie Captions Movie S1 Steam generation under simulated sunlight of 10 kw m -2. The 3DG material of 15 mm in diameter were floating on the interface of the water/air. Due to its low density and high hydrophilicity, the material can flow on the water and saturated with water 20

21 automatically without any further fabrication or supporting part. The steam was generated immediately once the light is on. Movie S2 Steam generation under monochromatic light of 10 kw m -2. The test was carried out in the same condition as the case using the simulated sunlight. The wavelengths of the monochromatic lights are 450, 532 and 650 nm. The steam was generated immediately once the light is on. Movie S3 Sewage treatment under simulated sunlight. The 3DG material and sewage water (methyl orange solution) were placed in the middle of the chamber. The steam was generated under the irradiation and then condensed into liquid when it arrived at the cold condenser. The condensed water automatically flowed along the container glass surfaces into the condensing receptacle under gravity. Finally, the clean water was collected. Movie S4 IR photograph of temperature distribution. An IR camera was used to investage the surface temperature of the 3DG under the 10 kw m -2 compared with the pure water. After the light illumination, in the absence of the 3DG, the pure water showed only a slow and small temperature rise. On the other hand, the temperature of the 3DG material rose sharply, indicating good solar-thermal performance of the 3DG, which is rationalized to the great solar absorbance and low specific heat capacity of the 3DG. 21

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